Lecture Notes on Domain Name System (DNS) and Related Topics

Introduction to DNS

• DNS as an Intermediary: Translates IP addresses into human-readable host names or domain names.
• Database Nature of DNS: DNS is a distributed and resilient database.
  • Distribution: DNS information is stored across different name servers.
  • Resilience: Globally available, exemplified by services like AWS Route 53.

AWS Route 53

• Services Offered:
  • Domain registration and hosting.
  • Ability to register a new domain or import an existing one.
• Hosted Zones:
  • Public Hosted Zones: Routes internet traffic globally.
  • Private Hosted Zones: Routes traffic within a specific VPC, used for internal company domains.

DNS Record Types

• Records as Instructions: They provide information on how traffic should be routed.
• Types of Records:
  • Name Server (NS) Records: Identify name servers in a hosted zone.
  • A and AAAA Records: Map hostnames to IP addresses (A for IPv4, AAAA for IPv6).
  • Canonical Name (CNAME) Records: Create shortcuts to route traffic to another domain.
  • TXT Records: Verify domain ownership, not typically used for routing traffic.

Time to Live (TTL)

• Purpose: Specifies how long DNS records should be cached by resolvers.
• High TTL: Used when data changes infrequently.
• Low TTL: Suitable for frequently changing data or during migrations.

DNS Routing Policies

• Simple Routing Policy: Directs traffic to a single resource, does not support health checks.
• Failover Routing Policy: Routes traffic to a primary resource and fails over to a secondary if the primary is unhealthy, supports health checks.
• Weighted Routing Policy: Distributes traffic based on set weights, useful for testing new versions of applications.
• Latency-based Routing: Routes traffic to the endpoint that offers the lowest latency.
• Geolocation Routing: Routes based on the geographical location of the user.
• Geoproximity Routing: Focuses on routing based on physical distance to the endpoint.

Hands-On Simulation

• Setup Overview:
  • Create EC2 instances, VPCs, and security groups.
  • Configure a load balancer and Route 53 records.
  • Integrate CloudFront for content delivery and caching.
• Key Steps:
  • Create a public certificate with AWS Certificate Manager (ACM) for secure connections.
  • Setup a CloudFront distribution with alternate domain names.
  • Use Route 53 to create simple and failover routing policies.
  • Simulate failover by stopping the primary instance and observing traffic routing to the secondary instance.

Key Takeaways

• The importance of understanding the DNS ecosystem and how different components like Route 53, load balancers, and CloudFront interact.
• The need for secure and efficient domain management using tools like AWS.
• Practical skills in setting up DNS configurations, routing policies, and understanding their implications in real-world applications.